Electrical inductive apparatus

ABSTRACT

Power transformer having a three section primary winding adaptable to various connection arrangements for providing different voltage ratings. A middle section is axially positioned between two end sections. The middle section has a voltage rating equal to one half of the desired voltage rating range and includes a center-tap terminal. Jumper connections are connected between taps on the winding sections to change the overall voltage rating of the winding. One pattern of connections places all or part of the middle winding section in series and in phase with the other winding sections to increase the voltage rating. Another pattern of connections places all or part of the middle winding section in series and antiphase with the other winding sections to decrease the voltage rating. The middle winding section may be bypassed completely to provide the nominal voltage rating of the transformer winding.

United States Patent n91 Golaski 1 March 6, 1973 [54] ELECTRICAL INDUCTIV FOREIGN PATENTS OR APPLICATIONS APPARATUS 1,264,600 3/1968 Germany ..336/150 [75 Inventor: Frank Colaski, Youngstown.

Ohio Primary Examiner-Thomas J. Kozma Attorne A. T. Stratton [73] Assignee: Westinghouse Electric Corporation, y

Pittsburgh, Pa. 57 ABSTRACT [22] Filed: 1971 Power transformer having a three section primary [21] Appl. No.: 192,523 Winding adaptable to various connection arrangements for providing different voltage ratings. A middle section is axially positioned between two end sections. [52] US. Cl. ..336/146, 323/43.5,333263/1458d The middle section has a voltage rating equal to one H0 1f 02 half of the desired voltage rating range and includes a [51] Int. Cl. 180 1/82 cememap terminaL Jumper connections are com [58] held of Search 2 146' 5 5 43 nected between taps on the winding sections to l I change the overall voltage rating of the winding. One pattern of connections places all or part of the middle 5 R fereh es Ci d winding section in series and in phase with the other wIndIng sections to Increase the voltage rating. UNITED STATES PAT NT Another pattern of connections places all or part of 2 840 790 6/1958 vogelet al 336/150 the middle winding section in series and antiphase 3182248 5/1965 McNamee :3 X with the other winding sections to decrease the volt- 2:253:l65 8/1941 Beymer.... ..323/48 g rating- The middle Winding sectiqn y be 1,057,077 3/1913 Moody.... ...336/147 X bypassed completely to provide the nominal voltage 2,994,030 7/1961 Diebold ..323/48 X rating of the transformer winding. 3,484,727 12/1969 Weber et al ..336/l47 3,162,799 12/1964 Roberts ..323/435 X 1 Claim, 3 Drawing Figures I II FL I 1 Pmamanm ems 3,719,910

SHEET 10F 2 I \0 o O o o Q 36 38 I l 4 22 FlG.l. 44 42 I PATENTEDMAR 6|973 C DE SHEET 2 OF 2 ELECTRICAL INDUCTIVE APPARATUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates, in general, to electrical inductive apparatus and, more specifically, to power transformers having winding arrangements adaptable for various voltage ratings.

2. Description of the Prior Art Many types of power transformers having windings which may be altered to produce a different voltage rating. Most of these transformers have tapped windings which may be interconnected in different arrangements before or after being energized.

A tap arrangement widely used in power transformers uses two high voltage windings sections with two intermediate tap terminals connected to each winding section. The tap terminals are locatedvnear the end of the winding section which is adjacent to the tapped end of the other winding section. With this arrangement, the voltage rating of the high voltage winding may be increased or decreased by 5 in 2%percent steps. This is usually accomplished by connecting jumper connectors between the appropriate taps before the transformer is energized. For example, a transformer having a nominal high voltage, rating of 7,200 volts may be jumped to change its high voltage winding rating to 6,840, 7,020, 7,380 or 7,560 volts.

Although this tapping arrangement functions satisfactorily, it has certain inherent disadvantages. The number of tap terminals which must be jumped equals six; the four intermediate tap terminals and two end terminals. The probability of making a defective jumper connection increases with the number of tap terminals involved. The four intermediate tap terminals are made between the ends of the winding sections. This requires a splice or braze to be made within the winding section and increases the probability of defective joints and stray brazing material in the apparatus, and increases the labor required to form the taps. It is desirable, and it is an object of this invention, to provide a winding arrangement which gives the same tap range and tapping increment with a smaller number of tap terminals. It is also an object of this invention to provide a winding arrangement whereby a smaller number of tap terminals are connected to a winding section between the ends of the section.

In concentrically wound windings, some of the conductor turns of a coil are usually wound in a radial direction before progressing axially to the next coil, thus, a large portion of the conductor is not exposed on the outermost surface of the winding. When using the tapping arrangement according to the prior art, a definite amount of conductor turns must be positioned between the tap locations. To meet this criteria, many of the tap terminals are connected to a coil turn within the winding rather than to an outermost coil turn. It is also desirable, andit is another object of this invention,

to provide a winding arrangement wherein as few taps as possible are made on the inner turns of a coil of the winding.

Short circuit strength is an important factor in determining the usefulness of a power transformer. With the prior art winding arrangement, the physical size of the low voltage winding is related to the physical size of the high voltage winding. Since the low voltage winding tends to collapse under short circuit conditions, the sizes of the windings are important in determining their resistance to short circuit stresses. In other words, the smaller and more compact the winding is, the easier it is to secure and brace against short circuit stresses. Therefore, it is also an object of this invention to provide a high voltage tapped winding which requires less physical space than the prior art winding arrangement.

Leakage fluxes and stray fields are developed when a section of a winding is tapped-out by a jumper arrangement. The larger tapped-out or bypassed portion of the winding, the greater the losses of the transformer. Maximum winding bypass according to the prior art occurs when the jumper arrangement is connected for the lowest voltage rating. It is a further object of this invention to reduce, over the prior art, the maximum winding which will be bypassed, thus reducing the losses of the power transformer.

SUMMARY OF THE INVENTION There is disclosed herein a new and useful arrangement for constructing a power transformer having a winding structure which can be interconnected in various arrangements to provide different voltage ratings. The winding is divided into three axially adjacent winding sections. The middle winding section includes a center-tap terminal and has a voltage rating equal to one-half of the desired voltage rating range of the entire winding. An end terminal for each of the two outside winding sections, the two end terminals of the middle winding section, and the center-tap terminal may be interconnected in various arrangements to provide different ratings for the overall winding voltage.

By the teachings of this invention, a maximum of only five terminals need be provided to change the voltage rating the same amount as the six terminals required according to the prior art. In addition, only one tap is connected between the end terminals of the winding sections whereas there were four according to the prior art. This makes connecting the taps easier and reduces the problems associated with intermediate tap connections. As a direct result in the reduction of intermediate taps, the probability of having to connect a tap near the inside of a coil turn in substantially reduced. In fact, with three less intermediate taps according to this invention, the probability is reduced to approximately one-fourth of the value according to the prior art arrangement.

Additionally, the overall winding dimensions are reduced, thus allowing a reduction in the size of the low voltage winding. This gives an inherent increase in short circuit strength. Stray transformer losses are also reduced by the fact that the maximum floating winding section according to this invention is only one-half that of the prior art arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of this invention will become more apparent when considered in view of the following detailed descriptionand drawings, in which:

FIG. 1 is a sectional view of a single phase transformer having a high voltage winding structure constructed according to the teachings of this invention;

FIG. 2 is a schematic diagram of a transformer constructed according to the teachings of this invention; and

FIG. 3 is a table illustrating some of the possible terminal interconnections which may be used to change the voltage rating of the transformer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar members in all figures of the drawing.

Referring now to the drawing, and FIG. 1 in particular, there is shown a sectional view of a single phase power transformer. A laminated magnetic core of the cruciform type is secure by the top end frame 12 and the bottom end frame 14. The locking plates 16 and also help to hold the laminations of the core 10 together with the use of the bolts 18 which project through the core 10.

In the sectional view of FIG. 1, the low voltage or secondary winding 20 is positioned concentrically around a leg of the magnetic core 10. Spacing rods 22 center the secondary winding 20 and help prevent collapse of the winding structure under short circuit stresses. The high voltage or primary winding structure 24 is concentrically disposed around the secondary winding 20 and comprises: a plurality of radially disposed conductor turns which form an array of coil disks stacked in an axial direction. The primary winding 24 is secured and compressed by the pressure blocks 26 and the pressure rings 28.

The winding structures 20 and 24 which are shown disposed on the magnetic core 10 have similar counterparts in the windings 30 and 32, which are disposed on the other core leg. An insulated barrier 34 separates the winding structures. Although coil disk interconnections, radial spacers, and tap terminals are not illustrated relative to the winding 24, it is to be understood that they may be present as illustrated in relation to the winding 32 and as will be described hereinafter in more detail. The main leads of the windings are not shown for clarity of the figure, however, the main lead arrangement may be such that the separate leg windings may be connected in series or in parallel circuit relationship. It is also within the contemplation of this invention that the primary winding 32 may be disposed on a core leg of a multiple phase transformer core.

The high voltage or primary winding 32 comprises three winding sections. The tap terminals 36, 38, 40, 42

and 44 provide means for interconnecting the winding sections. Jumper connections are usually used for this purpose and may be attached to the proper terminal by nut and bolt means. The three winding sections are all concentrically disposed around the secondary winding 30, .with each winding section located in a different axial position from that of the other winding sections.

FIG. 2 is a schematic diagram illustrating the position of the tap terminals. The high voltage or primary winding 32 comprises the winding sections 46, 48 and 50. Typically, winding sections 46 and 50 will have the same number of turns, thus the same voltage rating. Also, the winding section 48 will have a lower voltage rating than either of the other two winding sections. In a standard form of such transformers, the winding section 48 has a voltage rating which is equal to 5 percent of the sum of the voltage ratings of the windings sections 46 and 50.

The reference letters A, B, C, D and E correspond to the tap terminals 36, 38, 40, 42 and 44 respectively. The tap terminal 36 is located at the end of the winding section 46 and the tap terminal 44 is located at the end of the winding section 50. The tap terminals 38 and 42 are located at the ends of the winding section 48 and the tap terminal 40 is located at the center of the winding section 48. The total voltage rating of the winding 32 which exists between the terminals 52 and 54 is dependent upon the connection arrangement of the jumper connectors.

The connection arrangement may be such to add or subtract part or all of the voltage of the winding section 48 to the other winding sections, or it may be such to bypass the voltage of the winding section 48 completely. FIG. 3 is a table representing some possible connection arrangements. The table of FIG. 3 is based on a middle winding section, such as the winding section 48, having a voltage rating equal to 5 percent of the sum of the voltage ratings of the other winding sections. Other voltage ratings are within the contemplation of this invention.

In the table of FIG. 3, when the tap terminal A is connected to the tap terminal D and the tap terminal B is connected to the tap terminal E, the voltage rating of the winding 32 is 5 percent below a predetermined nominal value. When A is connected to D and C is connected to E, the voltage rating is 2%percent below the nominal value. The nominal voltage rating is obtained when A is connected to E. Connection to the tap terminal C may be desirable to reduce the floating effects of the winding section 48. The decreases in rated voltage are obtained by connecting the winding section 48 with the other winding sections in a out of phase relationship. When they are connected in phase, an increase in the nominal voltage rating occurs. The increase is 2 /percent when A is connected to B and C is connected to E. The increase is a 5 percent when A is connected to B and D is connected to E.

With the embodiment of this invention shown and described herein, it is possible to change the rated voltage by 10 percent in 2% percent increments. Advantages over the prior art arrangements include the need for fewer jumper connections, a smaller number of tap terminals, the elimination of all but one tap connected to an inner turn of a coil disk, the elimination of all but one tap connected between winding section ends, the reduction of stray fields and losses by a smaller floating winding voltage, and the improvement in short circuit strength realized by reducing the physical size of the winding. Since numerous changes may be made in the above described apparatus and different embodiments of this invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description, or shown in the accompanying drawings, shall be interpreted as illustrative rather than limiting.

I claim as my invention:

1. Electrical inductive apparatus comprising a magnetic core, primary and secondary winding structures concentrically disposed around a leg of said magnetic core with said primary structure being positioned outermost from said magnetic core, said primary winding structure being divided into first, second and third winding sections, said second winding section being axlocated adjacent to the outside of the winding structure and adaptable for connection to each other by jumper connections, with the connection arrangement determining the voltage rating of said primary winding structure, the voltage rating of said second winding section being equal to one-half the voltage rating range of said primary winding structure. 

1. Electrical inductive apparatus comprising a magnetic core, primary and secondary winding structures concentrically disposed around a leg of said magnetic core with said primary structure being positioned outermost from said magnetic core, said primary winding structure being divided into first, second and third winding sections, said second winding section being axially located between said first and said third winding sections, said second winding section comprising first and second end terminals and a tap terminal, said first winding section comprising a third end terminal adjacent to said first end terminal of said second winding section, said third winding section comprising a fourth end terminal adjacent to said second end terminal of said second winding section, all of said terminals being located adjacent to the outside of the winding structure and adaptable for connection to each other by jumper connections, with the connection arrangement determining the voltage rating of said primary winding structure, the voltage rating of said second winding section being equal to one-half the voltage rating range of said primary winding structure. 